. The objective of this proposal is to investigate the feasibility of adapting a new technology originally designed for rapid sterility testing to the problem of detection of rare mammalian cells. There is a need for rapid convenient methods to detect and count rare cells to evaluate residual disease in cancer or to monitor viral disease by direct counting of infected cells. Current methods of low cytometry and PCR have limited sensitivity and do not allow visualization of the detected rare cell. The instrument which will be investigated has the analysis speed of a flow cytometer but works upon a solid substrate examining a surface of approximately 400 mm2 in 2 minutes. It is designed to detect a single low level fluorescent signal and uses an elegant series of discriminators to eliminate false positive results. Further, the locations of detected cells are stored so that the cell can be recalled for visual conformation under a microscope. If it is feasible to modify this instrument and use it with available labeling methods for rare cells of clinical importance, then this technology could form the basis for a diagnostic instrument with wide applicability in monitoring cancer therapies or in detecting rare virus laden cells. PROPOSED COMMERCIAL APPLICATION: Rapid methods of rare cell detection have a wide variety of clinical applications (cancer therapy, HIV, Genetic Testing). Therefore, an instrument with increased sensitivity and convenient operation has potential sales in a large number of hospitals and research centers worldwide.